The use of endoscopes for diagnostic and therapeutic indications is rapidly expanding. To improve performance, endoscopes have been optimized to best accomplish their purpose. Therefore, there are upper endoscopes for examination of the esophagus, stomach, and duodenum; colonoscopes for examining the colon; angioscopes for examining blood vessels, bronchoscopes for examining the bronchi; laparoscopes for examining the peritoneal cavity; and arthroscopes for examining joint spaces. The discussion which follows will apply to all of these types of endoscopes.
Instruments to examine the rectum and sigmoid colon, known as flexible sigmoidoscopes, are good examples of the usefulness of endoscopic technology. These devices are expensive, and they are used in a contaminated environment for a brief procedure (5-10 minutes) to screen symptomatic and asymptomatic patients for colon and rectal cancer. Typically, these endoscopes have a flexible insertion tube that is inserted into a patient during an endoscopic procedure. During insertion, the position of the distal end of the insertion tube is controlled by control devices on the endoscope's handle at the proximal end of the insertion tube. The distal end of the insertion tube must be sufficiently flexible to bend through tight radius comers during insertion.
The endoscopes also have multiple channels that extend along the length of the endoscope and come into contact with body tissues and fluids during the endoscopic procedure. These channels allow air insufflation into a body cavity, water flow to wash the endoscope's tip, suction through the tip, and biopsies to be taken. The channels must be sufficiently flexible to bend with the insertion tube through the short radius turns. The channels also must substantially maintain their cross-sectional shape and resist kinking around the tight turns to assure continuous the air flow, water flow, suction, and biopsy capabilities throughout the procedure.
Endoscopic accessories that, for example, take tissue samples are inserted through one of the channels, known as a biopsy channel, and extend beyond the insertion tube's distal end. The endoscopic accessories typically have elongated flexible shafts and a tool operatively connected to the shaft's distal end. The shaft must be longer than the endoscope to extend through the biopsy channel; for example, in colonoscopy, the sigmoidoscope is up to 2 meters long. Accordingly, the biopsy channel must allow for the passage of the endoscopic accessory therethrough without binding or hanging up around the short radius corners. The biopsy channel also must be constructed to avoid damage by the accessory's tool during its passage, and to provide minimum frictional resistance between the biopsy channel's inner lumen and the endoscopic accessory.
Endoscope assemblies have incorporated channels, such as the biopsy channel, within the insertion tube so the longitudinal axis of the channel is coaxially aligned with neutral bending plane of the insertion tube. Additionally, the conventional endoscope channels can slide axially within the insertion tube of the endoscope during articulation. As a result, the amount of expansion and contraction the axial sidewalls of the channel experiences is minimized during acute endoscope articulation. Thus, the forces causing the channel to kink are minimized. Conventional working channels have thick walls along their entire length and are sufficiently stiff to obtain a degree of kink resistance. Additionally, the thick wall provides a more wear resistant surface as endoscopes typically have a four year life during which several thousand procedures can be performed. Conventional channels are typically manufactured from Teflon.RTM. which provides a high degree of lubricity but needs added support in the bending section to articulate without kinking.
Endoscopes have used biopsy channels with Teflon forming the inner lumen along the entire length of the channel to provide increased lubricity. However, the Teflon channels are not sufficiently durable for multiple endoscopic procedure and cleaning cycles. In addition, the Teflon channels have limited flexibility and axial expansion characteristics, and they are expensive to manufacture.
As disclosed in U.S. Pat. No. 4,676,229, other endoscopes have an integral biopsy channel with an internal lubricious layer of material forming an inner lumen that is disposed within and supported by an axially wound filament. A blanket material fills the area between the windings of the filament, and a kink resistant yet stiff outer coating surrounds the filament and blanket material. This sandwiched filament construction is also coaxially aligned with the neutral bending plane of the endoscope, and it extends along the entire length of the biopsy channel, resulting in a relatively stiff structure that allows a minimum degree of axial expansion or contraction of the channel's sidewalls during acute endoscope articulation. In addition, this construction results in a complex and heavy assembly that is expensive to manufacture.
Those endoscopes having integral working channels along the neutral bending plane are severely contaminated during an endoscopic procedure. Proper cleaning and sterilization of the insertion tube and the integral work channels is very laborious and costly, thereby reducing the cost effectiveness of performing the therapeutic or diagnostic endoscopic procedures.
Disposable endoscopic sheaths have been developed to alleviate the problem of cleaning and sterilizing the working channels. The disposable sheaths fit over the insertion robe and completely isolate the insertion tube from the contaminating environment. The isolated insertion tube does not have integral working channels, but does contain a visual imaging device, illumination devices, and the control wires that bend the insertion tube's distal end. Working channels, such as air, water, and biopsy/suction channels, are disposed within the sheath adjacent to the isolated insertion tube and are open of the sheath's distal end to allow passage of air, water, suction or endoscopic accessories through the channels.
As a result, these working channels are positioned radially outward of the neutral bending plane of the insertion tube. When the insertion tube is bent around a short radius comer, the working channels must bend about the radially spaced neutral bending plane of the insertion tube so the axial sidewalls of the working channels are subject to significant axial expansion and compression forces which may cause kinking. Accordingly, the working channels must be axially flexible so the axial walls will expand and contract and will not kink or substantially resist the bending action of the insertion tube.
The Teflon biopsy/suction channel with the sandwiched filament section as well as the air and water channels discussed above are not suitable for use in such an endoscope/sheath assembly, because they are not sufficiently flexible and axially expandable. As a result, they would either kink or they would exert too much resistance to bending of the insertion tube around tight corners. Additionally, their construction is too expensive for a disposable product.
Accordingly, there is a need to provide an endoscopic sheath assembly having working channels that are flexible and axially expandable at their distal end so as to expand and contract as the channels bend about a remote neutral bending plane, thereby allowing the channels to bend without kinking and to exert a minimum degree of bending resistance on the endoscope. There is also a need for endoscope working channels with a durable lubricious inner lumen that allows for easy passage of an endoscopic accessory therethrough, an external surface that facilitates inserting and removing the endoscope. There is yet a further need for working channels that are inexpensive to manufacture so they can be used with a disposable endoscopic sheath and be disposed of after a single use.